1. Field of the Invention
The present invention is related to a method of polishing a substrate using a polishing tape having a fixed abrasive, and more particularly to a method of polishing a peripheral portion of a substrate using the polishing tape.
2. Description of the Related Art
In semiconductor device fabrication, various materials are deposited in the form of film on a wafer repeatedly to constitute a multilayer structure. This multilayer structure is formed not only on a surface of the wafer, but also on a peripheral portion of the wafer. The peripheral portion of the wafer is a region which is not used for products. It is necessary to remove a film on the peripheral portion, because the film on the peripheral portion would be peeled off during transporting of the wafer and would then adhere to device regions on the wafer, causing a lowered yield. Thus, in order to remove the film on the peripheral portion of the wafer, polishing of the peripheral portion is performed, as disclosed in Japanese laid-open patent publication No. 2001-345294.
In polishing of the wafer having the aforementioned multilayer structure, there exists a process of selectively removing only an upper film. In such a process, it is necessary to selectively remove only the upper film by polishing it, without removing a lower film lying beneath the upper film.
A polishing method using a polishing tape is widely known as a method of polishing a peripheral portion of a wafer. For example, Japanese laid-open patent publication No. 2003-163188 discloses a method of polishing a peripheral portion of a substrate using a polishing tape having a fixed abrasive. However, use of such a polishing tape may roughen a surface of the substrate as a result of contact with the fixed abrasive.
Japanese laid-open patent publication No. 2004-103825 discloses a method of polishing a peripheral portion of a substrate by bringing a polishing cloth into contact with the peripheral portion while rotating the substrate and supplying a polishing liquid containing abrasive grains onto the substrate. In this method, the abrasive grains are suspended in the polishing liquid, i.e., in a loose state, and therefore less likely to make polishing scratches on the surface of the substrate. However, the loose abrasive grains may adhere to semiconductor devices on the substrate due to the rotation of the substrate. In order to remove such abrasive grains, it is necessary to wash the substrate with a powerful cleaning liquid after polishing of the substrate. Moreover, use of such a powerful cleaning liquid is not allowed in some processes.
In contrast, the above-described polishing method using the polishing tape having the fixed abrasive does not need using such a powerful cleaning liquid, because a polishing liquid (slurry) is not supplied to the substrate. Therefore, this polishing method is more suitable for the fabrication of the semiconductor devices. However, since an area to be polished in the peripheral portion of the substrate is small, a narrow polishing tape is necessarily used. As a result, a polishing rate decreases. In order to improve the polishing rate, a polishing tape using diamond abrasive grains may be used. However, as described previously, use of the diamond abrasive grains could roughen a surface of the substrate. In order to avoid such a rough surface, it is necessary to perform multistep polishing using multiple polishing tapes having small abrasive grains with different sizes. However, such multistep polishing takes a long time and therefore a polishing time in its entirety becomes long. As a result, a process efficiency is lowered.